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1_ Lewis Dot Diagrams

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									Lewis Dot Diagrams
  Try Nitrogen and Gallium
1) Lewis Dot Diagrams
 another way to show electron
 configuration




                       G. N. Lewis
 also allows us to   visually represent
                       1875 - 1946
  bonds and molecule shape
 named after G.N. Lewis
1) Lewis Dot Diagrams
 diagram creation



                     Cl
   write the atomic symbol
   imagine 4 orbitals around the symbol
     each orbital can hold 2 e- (max)
   put dots in, to represent valence e-
     put one electron In each orbital before
      doubling up
   # dots = # valence electrons
    1) Lewis Dot Diagrams
Electrons are divided between core and valence
  electrons
                    for Lewis Dot Diagrams:
                valence e- are only those in the
               highest principle quantum number

                       B - 1s2 2s2 2p1
                      valence = 2s2 2p1

                    Br [Ar] 4s2 3d104p5
                                                     Br
                     valence = 4s2 4p5
this way Lewis Dot Diagrams will normally have 8 e- (ie, dots) max
1) Lewis Dot Diagrams
recall:
   Atoms like to either empty or fill their
    outermost level.
   Since the outer level contains two s
    electrons and six p electrons (d & f are
    always in lower levels), the optimum
    number of electrons is eight.
   This is called the octet rule.
1) Lewis Dot Diagrams
 examples
      O




             O   O
      H


                     He



       Ne
 1) Lewis Dot Diagrams
   vocab:
                                  a lone pair of e-
                                        or just
                                     “lone pair”



                    O
bonding electrons

                    note: all of the dots are valence e-

   so…oxygen has 2 lone pairs and 2
    bonding electrons (6 valence e-)
              2) So What?
 drawing atoms in this way helps us
  understand covalent bonds

                  recall:
       covalent bonds - sharing of e-
         ionic bonds - transfer of e-

 these diagrams are not as useful with ionic
  bonds
 ions in ionic bonds already have full octets
   Lewis diagrams would be pretty boring
                 2) So What?
 we call them “bonding electrons” for a reason

                     Cl needs 1 more e-
 consider:


              H                          Cl
                     H needs 1 more e-
   how many e- does H need to be “happy”?
   what about Cl?


 these two “unhappy” atoms can work together to
  both be “happy” by SHARING their bonding e-!
               2) So What?

         H                           Cl
electrons in different “unhappy” atoms will rearrange
 themselves, and form bonds to become “happy”!




                   H Cl
H is happy                                Cl is happy
it has 2 e-                               it has 8 e-
 notation note:
    to show where the e- originally came from, we often
     use x’s and o’s to distinguish between electron origin



             H Cl = H Cl                    x



    we also show the e- between atoms (the bonding e-
     ) as a line

                      H- Cl
                   shared or bond pair e-

 This is the the LEWIS STRUCTURE of HCl.
3) Steps to Build a Lewis Structure
1. Draw the lewis stucture of the central atom
   (normally the “single” atom)




                                  N
 1 Ns in NH3                                 3 Hs in NH3




                     N is the central atom
3) Steps to Build a Lewis Structure
2. Draw the other atoms around the central one




          H   x         N               H      x




                        H   x


2. Start pairing up the electrons   (using circles or lines)
3) Steps to Build a Lewis Structure
4. Carefully redraw the bond pairs as lines.




          H   x         N           H   x




                        H   x

5. If needed, move electrons around to keep
    octets (more on this later)
NOTE:
             H N H x
                            x
                       x

               H            a bond is just a pair
                            of electrons

  NH3 has 3 bond pairs and 1 lone pair
  of e-

  notice: each atom is now “happy”
     each H has 2 e- and the N has 8 e-
                Try It!
 Draw the Lewis dot structure for:

  H2O
               be sure to follow the steps!
  CH4
                Homework
           page 244:
            #1-5

           read page 243 - 246

Draw the Lewis Structure for:
H2O2                       each atom has an octect

CO2

								
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